Chesapeake Bay Winds of Change

Grass blowing in wind

Winds of Change By Tom Pelton

From the early days on the Chesapeake Bay to the yacht races held all along the Bay today, the Chesapeake’s winds have played an outsized role in the region’s economy and culture.

But some scientists have concluded that those wind patterns have undergone a historic shift. And this change in average wind direction has had an impact not only on sailing, but also on water quality in the Bay. Until about 30 years ago, the prevailing winds that blew up the Bay in the summertime came mostly from the south, according to Dr. Michael Kemp, a professor at the University of Maryland Center for Environmental Science.

These southerly winds would sweep the 200-mile length of the Bay. Winds that run in this direction are unobstructed by trees or land masses, which allows them to build up speed, make waves, and stir oxygen into the Bay’s waters. But then this mixing machine broke down.

“Starting probably in the mid 1980s to the present, we’ve seen the winds moving around primarily from…the west,” Dr. Kemp said. “We still get southerly winds. But we get a much higher frequency of winds out of the
west, which has a very different impact.” The Bay is narrow from west to east—about 4 miles across near the Bay Bridge. So winds from the west do not have much room to make waves and stir the high-oxygen
surface water into the oxygen poor depths. This reduced circulation of oxygen makes it harder for oysters, clams, worms, and other critters on the bottom to survive. Low-oxygen “dead zones” are caused by
water pollution—nitrogen and phosphorus from sewage plants, farms, lawns, and other
sources. But the right kinds of winds and currents can help breathe life back into suffocating

The shifting wind patterns appear to be caused by a giant El NiƱo-like weather pattern over the Atlantic Ocean, called the North Atlantic Oscillation, which shifts every few decades, according to Dr. Malcolm Scully, an oceanographer at Old Dominion University, who wrote about the subject in an article for the Journal of Physical Oceanography.

Recently, there have been signs that this pattern may be shifting back again, which could mean a return of more powerful southerly winds, better water circulation, and a reduction of the dead zones, Dr. Scully said.

“The extent and severity of these dead zones appears to be very sensitive to what the wind climate is like,” said Dr. Scully. “And it could be that we’ve just now entered into a period in which we are going to have a different wind climate.”

This could mean good news for water quality. But Dr. Scully said that the fact that winds affect water quality doesn’t mean that we shouldn’t care about pollution. Just the opposite, in fact, it meanswe have to be even more diligent about reducing pollution, because that’s the one factor we can control. Reduced nitrogen
and phosphorus pollution, combined with better water circulation, could mean a substantially healthier Bay.

Tom Pelton is Senior Writer for
the Chesapeake Bay Foundation.
His daily blog on current Bay
issues can be found at

Winds of Change By Tom Pelton sourced from Save The Bay Magazine Fall 2010

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